1. Field of the Invention
The present invention relates to a system for monitoring a plurality of objects in a predefined detection area, comprising:                a plurality of radiofrequency identification tags, each tag being suitable for being attached onto an object,        at least one radiofrequency reader for reading radiofrequency identification tags, the or each reader being connected to an antenna, and all of the readers defining the predefined detection area,        a means for processing information transmitted by the or each radiofrequency reader, the information comprising an identifier specific to each tag to be monitored in the predefined detection area, and        an alarm means connected to the processing means.        
The invention applies to the field of monitoring goods or people.
Such systems make it possible to detect and quickly signal the disappearance or excessive removal of an item or an individual with respect to a predefined area.
For example, such systems are used in the maritime field, to monitor people and verify that they have not fallen overboard.
The systems must have a reduced size and weight so as for example to be integrated into equipment (sailing jackets, boots or in the form of bracelets, etc.). Furthermore, they must eliminate or minimize the need for human intervention.
2. Description of the Related Art
A maritime monitoring and alarm system is described in patent application US 2009/0219160 A1. This includes radiofrequency identification tags that use the RFID (radiofrequency identification) technology. These radiofrequency identification tags are worn by a person present on the boat. The system further comprises radiofrequency readers connected to directional aerials whereof the detection range for the radiofrequency identification tags delimits a monitoring and safety area.
One of the drawbacks of this system is that all of the radiofrequency identification tags, irrespective of whether they are associated with an object to be monitored, transmit and receive radiofrequency signals so as to identify them with radiofrequency readers integrated into the system. Thus, a significant stream of useless signals, i.e., those regarding tags not associated with an object to be monitored, is generated.